I performed the ITC (isothermal titration calorimetry) experiments by titrating the LUVs made of POPC and POPG into the daptomycin solution. After exporting the data in the Excel, I used the Origin for the fitting the curves in order to find the binding constant. No function fitted that well as the biphasic dose response function, but the x axis is in my case is linear, and not logarithmic. Is it allowed to leave as linear-scaled?
Thank you very much for the responses
Even if a certain function can reproduce the experimental data, this does not allow you fitting the data with that function, because the parameter estimations you get may be meaningless. I am sure you can fit the data with many functions, even with a high-order polynomial. The dose-response function is not appropriate, for many reasons.
You must couple appropriate interaction model equations with the instrumental equations, and from that you will be able to get valuable information for your system.
In addition, there is no justification to consider a biphasic isotherm. What you observe around molar ratio of 5-7 is within experimental uncertainty.
Mathematically, you "cannot" leave x scale linear as it is if you use "logarithm form" biphasic dose response function to fit the isotherm. You can try to fit the data using "linear form" biphasic dose response function. It is a simple scale transformation. As far as I know, the two biphasic dose response functions are both available in GraphPad Prism.
However, as Adrian Velazquez-Campoy mentioned, whether or not the fitting parameters you got make any sense, it depends on a thermodynamic model beyond the fitting.
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